Counties in Delaware New Castle County Map, Delaware Vishal KumarAugust 16, 202202K views Facts about New Castle County County New Castle State Delaware Country USA Population – 2015 556,779 List of Counties in Delaware County Name County Seat/Capital State 2010 pop. Area-km… Buy Printed MapBuy Digital MapWall MapsCustomize Facts about New Castle County County New Castle State Delaware Country USA Population – 2015 556,779 List of Counties in Delaware County Name County Seat/Capital State 2010 pop. Area-km Area-mi Kent Dover Delaware 1,62,310 1,518 586 New Castle Wilmington Delaware 5,38,479 1,104 426 Sussex Georgetown Delaware 1,97,145 2,424 936